Bottom Line:
The self-assembly of salt nanocrystals from chemical reactions inside liquid helium is reported for the first time.Reaction is initiated by an electron impacting a helium nanodroplet containing sodium atoms and SF6 molecules, leading to preferential production of energetically favorable structures based on the unit cell of crystalline NaF.In the case of anions the self-assembly is not directly initiated by electrons: the dominant process involves resonant electron-induced production of metastable electronically excited He(-) anions, which then initiate anionic chemistry by electron transfer.

fig01: A section of the cation mass spectrum obtained from electron-induced reactions between Nan and (SF6)m clusters. This mass spectrum was recorded at an electron energy of 100 eV.

Mentions:
The major cationic products can be divided into two types: (NaF)nNa+ and (NaF)n(Na2S)mNa+. By way of contrast the stoichiometric (NaF)n+ cluster ions are more than an order of magnitude less abundant than the (NaF)nNa+ ions. A small quantity of (NaF)nNa+ ions with added helium atoms were also observed, as can be seen in Figure 1. The survival of these adduct ions suggests that at least some of the cluster ions produced are ultimately cold enough to retain one or more helium atoms.

fig01: A section of the cation mass spectrum obtained from electron-induced reactions between Nan and (SF6)m clusters. This mass spectrum was recorded at an electron energy of 100 eV.

Mentions:
The major cationic products can be divided into two types: (NaF)nNa+ and (NaF)n(Na2S)mNa+. By way of contrast the stoichiometric (NaF)n+ cluster ions are more than an order of magnitude less abundant than the (NaF)nNa+ ions. A small quantity of (NaF)nNa+ ions with added helium atoms were also observed, as can be seen in Figure 1. The survival of these adduct ions suggests that at least some of the cluster ions produced are ultimately cold enough to retain one or more helium atoms.

Bottom Line:
The self-assembly of salt nanocrystals from chemical reactions inside liquid helium is reported for the first time.Reaction is initiated by an electron impacting a helium nanodroplet containing sodium atoms and SF6 molecules, leading to preferential production of energetically favorable structures based on the unit cell of crystalline NaF.In the case of anions the self-assembly is not directly initiated by electrons: the dominant process involves resonant electron-induced production of metastable electronically excited He(-) anions, which then initiate anionic chemistry by electron transfer.